Is continuously seeding a random number generator performance intensive?

[monarch_dodra]

On Thursday, 2 January 2014 at 20:38:10 UTC, Jeroen Bollen wrote:
> D provides a set of Random Number Generators in std.random. I 
> am writing an application which would create a 2D map of noise. 
> To do this though, I'll have to calculate the same random 
> numbers over and over again. (I cannot store them, that'd take 
> a horrible amount of RAM. )

AFAIK, the costliest part of seeding a generator is generating 
the "random seed". After that, once you have the seed, it 
shouldn't be too expensive. That said, it depends on each 
generator of course. In any case, performance wise, it shouldn't 
be too expensive (if you use the same seed).

That said, it sounds like what you want to do though is to simply 
"save" the range. PRNG's have the "save" primitive you can use. 
Just use that.

> Is it good to re-seed a generator for every coordinate, will 
> this be performance intensive? Is there maybe way to easily 
> implement Generator.at(uint x) in D?

*This* comment is confusing me. What do you mean by "re-seed"? 
You mean a random seed? Once seeded, you shouldn't have to 
re-seed a PRNG: It'll generate random numbers forever. Or do you 
mean "re-seed" in the sense "reset"? Because if you do that, then 
you'll have the same numbers for each coordinates...?